Experiments and Simulations of Escherichia coli Chemotaxis
Title: Experiments and Simulations of Escherichia coli Chemotaxis
Students: Giovanni Giammanco and Gregory Walls
Advisors: Dr. Frank Healy and Dr. Hoa Nguyen
Abstract: For certain bacteria such as Escherichia coli, bidirectional propeller-like rotary motion of flagellar filaments results in the net movement of the cell through gradients of chemoattractant molecules toward areas of higher attractant concentrations. Directional switching of the flagellar motor is governed by a phosphorelay circuit that transfers phosphoryl groups from donor to acceptor proteins; and protein phosphorylation state is controlled by binding of chemoattractants to specific receptors. The two-dimensional hydrodynamics of cell motility is modeled by coupling the chemotaxis equations of a simplified phosphorylation cascade with the method of regularized Stokeslets of the fluid motion. For a slow enough diffusion rate of the attractant gradient, simulations have consistently resulted in a biased random walk of the majority of cells towards the highest concentration of attractant, chemotactic behavior. Using GFP expressing E. coli and confocal microscopy, the motion and chemotaxis behavior can be tracked and analyzed to validate a model. The results from the model and experiment demonstrate how the phosphorylation affects the run and tumble mechanism of swimming bacteria.